The present invention relates, in general, to electronics and, more particularly, to methods of forming semiconductor devices and structure.
Power storage units are used in many applications including automotive, aerospace, airline, nautical, computer, communications, heavy equipment, remote sensing, etc. The power storage units may serve as a power supply or a battery that provides a particular rated voltage to drive an electrical load. The power storage units may be comprised of a number of individual battery cells that are connected in parallel or in series. The lifetime of the battery is strongly dependent on the way in which the battery is charged and discharged and will be reduced by over-charging the cells or over-discharging the cells. In addition, it is desirable to keep all the cells of a battery stack at the same capacity. This corresponds to keeping all the cells at about the same open circuit voltage. Use of the battery and over-discharge of one cell will impact the lifetime of that cell and of the battery. Battery manufacturers are constantly striving to find better and more accurate measurement techniques for measuring the voltage across battery cells. Along with improving measurement techniques, battery manufacturers are searching for ways to balance the cell voltages within a battery stack.
Accordingly, it would be advantageous to have a circuit and a method for monitoring and balancing the voltage of a battery stack and the voltages of the cells within a battery stack. It would of further advantage for the circuit and method to be cost efficient.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of being exactly as described.
It should be noted that a logic zero voltage level (VL) is also referred to as a logic low voltage or logic low voltage level and that the voltage level of a logic zero voltage is a function of the power supply voltage and the type of logic family. For example, in a Complementary Metal Oxide Semiconductor (CMOS) logic family a logic zero voltage may be thirty percent of the power supply voltage level. In a five volt Transistor-Transistor Logic (TTL) system a logic zero voltage level may be about 0.8 volts, whereas for a five volt CMOS system, the logic zero voltage level may be about 1.5 volts. A logic one voltage level (VH) is also referred to as a logic high voltage level, a logic high voltage, or a logic one voltage and, like the logic zero voltage level, the logic high voltage level also may be a function of the power supply and the type of logic family. For example, in a CMOS system a logic one voltage may be about seventy percent of the power supply voltage level. In a five volt TTL system a logic one voltage may be about 2.4 volts, whereas for a five volt CMOS system, the logic one voltage may be about 3.5 volts.